In communication satellites serving multiple users and in other applications having similar power constraints, it is desirable to have the capability to transmit signals at different strengths matched to the user's needs. The signal strength requirements of a particular satellite's users can vary greatly. For example, a low baud rate digital signal to be transmitted for one user may require much less transmission power than an analog television signal for another, due to different signal to noise ratio requirements for the two signals. Therefore, in order to utilize the satellite's limited power resources in an efficient and cost effective manner, it is beneficial to provide a power level appropriate for each user. It is known that by controllably varying the DC bias voltage levels to the satellite's rf amplifier stages, the transmission power of the satellite may be adjusted to meet a particular user's needs.
A multi-resonant DC-DC electronic power converter (MRC) is currently being employed to provide variable bias voltage levels. This MRC converts the satellite's high voltage DC bus into a DC output level. The output level is controlled by a switching frequency signal which is supplied to the MRC by a control circuit. The control circuit determines the switching frequency based upon the transmission power requirements.
The switching frequency signal drives a switching transistor in the MRC, which converts the satellite's high voltage DC bus into an AC voltage. The AC voltage is then processed by a simple LC low pass filter and thereafter converted back into DC. By choosing a switching frequency that falls on the gain slope region of the low pass filter, any adjustment in frequency will vary the dc output level. This prior art MRC, however, suffers from having a limited dynamic range of output levels.
The benefits of MRCs are not limited to satellite applications but are also desirable in many system applications where similar design constraints came into play. For example, portable and cellular telephones require various levels of power, depending on the distance between the transmitter and the receiver. An MRC would have similar advantages in those systems, as well as others.